Suitability of Translocation Sites for Florida Burrowing
Owls: Prey Availability and Diet
Ronald J. Sarno, Per A. Nixon, Brian K. Mealey, Ronald E. Concoby, Robert J. Mrykalo, and Melissa M. Grigione
Southeastern Naturalist, Volume 11, Issue 4 (2012): 755–764
Full-text pdf (Accessible only to subscribers. To subscribe click here.)
2012 SOUTHEASTERN NATURALIST 11(4):755–764
Suitability of Translocation Sites for Florida Burrowing
Owls: Prey Availability and Diet
Ronald J. Sarno1,*, Per A. Nixon2, Brian K. Mealey3, Ronald E. Concoby4,
Robert J. Mrykalo5, and Melissa M. Grigione6
Abstract - We investigated if relative abundance of invertebrate prey for Athene
cunicularia floridana (Florida Burrowing Owl) differed between two pre-translocation
(i.e., non-mined) sites and one translocation (i.e., reclaimed mine) site. We trapped a
combination of 21 arthropod families and orders. We observed some differences among
non-mined sites and the reclaimed mine site in invertebrate prey abundance and owl diet.
Fewer than 50% (10 of 21) of trapped prey items were present in pellets, suggesting that
our traps may have limited capture of particular prey. Additionally, it appears that owls
were hunting in nearby aquatic habitats due to the remains of frogs, turtles, and crayfish in
pellets. The general similarity in prey abundance and diet between the pre-translocation
and translocation sites suggests that reclaimed mine sites may serve as adequate refugia
for Florida Burrowing Owls. However, more work is needed to determine to verify the
general applicability of our results.
Introduction
Phosphate mining disturbs 2000 to 2500 ha/year in Florida, with nearly 2/3
of this area characterized as upland or mesic habitat (Florida Department of Environmental
Protection 2005). The vast majority of upland habitat is improved
pasture—pasture in which agricultural grasses or other forage species have been
introduced in order to increase the volume and quality of available grazing forage
for livestock (Florida Department of Transportation 1999). These habitats have
also been found to support populations of Athene cunicularia floridana (Molina)
(Florida Burrowing Owl) (Mealey 1997, Mrykalo et al. 2007), which have been
state listed as a species of special concern by the Florida Fish and Wildlife Conservation
Commission (FWC) since 1979 (Florida Department of State 1979) as a
result of population declines due to continued habitat loss (Birnhak and Crowder
1974, Ewel 1990). The FWC has recently recommended that the Florida Burrowing
Owl be upgraded to a state-listed threatened species (Florida Fish and
Wildlife Conservation Commission 2011).
Mining activities in upland habitats generally result in the displacement
of Florida Burrowing Owls. As a result, mining companies are required to restore
mined sites in accordance with local, state, and federal mandates (Florida
1Department of Biology, 228 Gittleson Hall, 114 Hofstra University, Hempstead, NY
11549. 2Department of Environmental Science and Policy, University of South Florida,
4202 East Fowler Avenue, Tampa, FL 33620. 3Institute of Wildlife Sciences, 16531 SW
81st Avenue, Palmetto Bay, FL 33157. 4Eco-Logic Restoration Services, LLC, 1517 Orange
Avenue, Eustis, FL 32726. 5PO Box 292452, Tampa, FL 33687. 6Graduate Program
in Environmental Science, Department of Biology, Pace University, Pleasantville, NY
10570. *Corresponding author: e-mail-Ronald.Sarno@hofstra.edu.
756 Southeastern Naturalist Vol. 11, No. 4
Statutes Chapter 378 and Florida Administrative Code Chapter 62C-16). Restoration
includes type-for-type, acre-for-acre replacement of specific habitats,
including Paspalum notatum (Alain ex Flüggé) (Bahia Grass) pasture for cattle
grazing. Avian surveys conducted on reclaimed mined sites between 1995 and
2005 suggest, however, that Florida Burrowing Owls do not recolonize these
sites (Concoby 2006a).
Translocation has been used as a management tool for relocating Burrowing
Owls to suitable habitat in California, Arizona, British Columbia, Oregon, and
Washington (Delevoryas 1997, Feeney 1997, Klute et al. 2003), and one of the
vital components for translocation success is food availability at the recipient site.
Prey remains identified in Florida Burrowing Owl stomachs (Bent 1938, Lewis
1973, Palmer 1896), regurgitated pellets (Hennemann 1980, Neill 1954, Palmer
1896, Wesemann 1986), and burrows (Hennemann 1980, Neill 1954, Nicholson
1954, Owre 1978, Wesemann 1986) indicate a broad diet, with major prey items
consisting of invertebrates, especially arthropods (Cahoon 1885, Mrykalo et al.
2009, Rhodes 1892, Ridgeway 1874, Sprunt 1954). Given the potential habitat
available for Burrowing Owls on reclaimed mined sites, coupled with the fact that
invertebrates comprise a substantial prey of Burrowing Owls, our primary objectives
were to (1) determine relative prey abundance/prey richness of invertebrates
on non-mined (pre-translocation) and reclaimed mine (translocation) sites, and
(2) quantify the diet of Florida Burrowing Owls inhabiting these two areas.
Mushinsky and McCoy (2001) reported that reclaimed mine sites generally
contain fewer vertebrates for approximately 3 years following reclamation. Using
this as a proxy for invertebrate abundance and considering that at least 15
years have elapsed from the time that the translocation site was initially mined,
we hypothesized that arthropod abundance/richness on the pre-translocation and
translocation sites would be equal.
Methods
The study was conducted from 15 May 2005 to 15 May 2006 at 3 locations:
2 pre-translocation (donor) sites, and 1 translocation (recipient) site. The pretranslocation
sites contained 9 pairs of Florida Burrowing Owls which were later
translocated. The pre-translocation sites were never mined and contained improved
pastures composed of Bahia Grass and natural soil. The translocation site
was a reclaimed phosphate mine converted to improved Bahia Grass pasture. The
translocation site had been mined a minimum of 15 years before this project. All
study sites contained third-order tributaries (creeks), and/or ephemeral wetlands
within 500 m of burrows. Since these pastures had been ditched and drained for
cattle use, the ephemeral wetlands were depressions that maintained drainage in
these areas.
The pre-translocation (donor) sites spanned two counties and were located
on Fort Lonesome East, Mining Units 16 and 17, east of SR 39, Hillsborough
County, FL; and Fort Green Mine, Manatee County Addition, Hardee County,
FL. These areas consisted of approximately 580 ha of typical improved pasture.
R.J. Sarno, P.A. Nixon, B.K. Mealey, 2012 R.E. Concoby, R.J. Mrykalo, and M.M. Grigione 757
The translocation (recipient) site contained artificial burrow systems, and was a
239-ha parcel located at Fort Green Mine, Polk County, FL. The translocation
site was designated as the Fort Green Mine Special Reclamation Project Area
and was located approximately 8 km southwest of the Fort Lonesome and Fort
Green Mine sites (Fig. 1).
A total of 9 release enclosures were designed, constructed, and installed on
the translocation site. Enclosures were modified from those used to translocate
Burrowing Owls at the Wild at Heart Rehabilitation Center, Cave Creek, AZ.
Enclosures were constructed from 1.27-cm schedule 40 PVC pipe frame that was
supported by wooden poles. The frame was covered with plastic cloth used for
shading cattle. Each enclosure was 8 m x 8 m x 3 m high. Within each enclosure,
R. Concoby (2006b) placed a single T-perch constructed from untreated 5.1-cm
x 10.2-cm lumber. Artificial burrow systems were constructed to mimic natural
burrows for translocated owls. Water bowls and a 45.7-cm x 45.7-cm food board
were positioned to allow ease of access for all owls. Owls were provided 8–10
crickets and 2 mice/burrow/day. Birds were released after 18 days. Fifteen burrowing
owls were successfully translocated. This effort resulted in nesting by 4
breeding pairs and the fledging of 9 juveniles that were produced from the original
translocation of the 4 breeding pairs.
Relative prey abundance and richness
We define relative abundance as the mean number of arthropods/family (or
order)/site. Relative richness is defined as the total number of arthropod families
(or orders)/site. We trapped each study site 2 times each month for 2 days during
each trapping occasion in order to assess relative abundance and richness of
Figure 1. Location of the Fort Green and Fort Lonesome Mining Units that contained the
pre-translocation (donor) and translocation (recipient) sites for Florida Burrowing Owls,
15 May 2005 to 15 May 2006.
758 Southeastern Naturalist Vol. 11, No. 4
potential prey items. We set 10 pitfall traps (i.e., 10 coffee cans, 15.24 x 17.8 cm,
buried flush with the ground) at each study site during each trapping occasion.
Each can contained 2.54 cm of soapy water in the bottom to prevent the escape
of insects (Wesemann 1986). Two pitfall traps were placed approximately 200 m
from 5 randomly selected burrows. Orientation (i.e., north, south, east, and west)
of insect traps from enclosures were obtained from a random number generator.
At the translocation site prior to translocation, we placed traps randomly within
the predetermined relocation areas by constructing a grid and generating random
x- and y-coordinates. All arthropods were counted and identified to the lowest
taxonomic group (family or order) at each site (Bland and Jaques 1978). Relative
abundance and relative richness on the two non-mined pre-translocation sites
were combined for analyses.
The total number of trapped insects from each site/trapping session was
normalized using a square-root transformation. We examined relative prey
abundance using an independent sample’s t-test to compare the mean number of
arthropods/family (or order)/site. For comparisons of prey abundance between
sites we utilized the Holm’s sequential Bonferroni correction (Holm 1979) in
order to reduce the probability of a type I error. Prey richness was analyzed using
a chi-square goodness-of-fit test on the total number of arthropod families (or
orders) trapped/site (Sokal and Rohlf 1994).
Diet analysis
Diet was determined from regurgitated pellets that were collected from each
site. Regurgitated pellets were collected up to 5 m from each active burrow at
least twice each month. Following field collection, pellets were dried in an incubator
at 70 °C for 48 hrs and dismantled. Prey contents were identified using a 10
x 3 dissecting stereomicroscope. We separated contents by prey type using easily
identifiable exoskeletal sections, such as mandibles, head capsules, and elytra
(Gleason and Craig 1979, Mrykalo 2005, Wesemann 1986). Arthropod exoskeleton
parts were identified to the lowest practical taxon by comparing them to
previously identified specimens at the University of South Florida. Vertebrate
items were identified by referencing a specimen collection at the Florida Museum
of Natural History. The total number of arthropods and vertebrate prey remains
in pellets was summed to indicate the frequency of prey items in the diet (Wakeley
1978). As for relative abundance and relative richness, the data from the two
non-mined pre-translocation sites were combined for analyses. We performed a
square-root transformation on the total number of arthropods and vertebrates in
each family (or order)/sample in order to normalize the data. Normalized totals
were analyzed using independent sample’s t-test in order to compare means
among sites (Sokal and Rohlf 1994). Holm’s sequential Bonferroni correction
(Holm 1979) was utilized to reduce the probability of committing a type I error
when comparing diet among owls in pre-translocation and translocation sites. A
Spearman’s rank-order correlation (Sokal and Rohlf 1994) was used to compare
the monthly means of trapped prey items/family/site to monthly means of prey
items/family/site found in pellets. All data were analyzed using SAS software
(SAS Institute, Inc. 2001).
R.J. Sarno, P.A. Nixon, B.K. Mealey, 2012 R.E. Concoby, R.J. Mrykalo, and M.M. Grigione 759
Results
Prey richness
There were no appreciable differences in relative prey richness between the
pre-translocation (non-mined) site and the translocation (reclaimed mine) site, as
we trapped a total of 21 different types of arthropods on the pre-translocation site
and 15 on the translocation site (χ 2 = 1.00, df = 1, P = 0.32; Table 1).
Prey abundance
As a result of the sequential Bonferroni control, the critical P-value at which
independent samples t-tests were no longer considered significant for prey abundance
was P > 0.025.
The pre-translocation site contained significantly more insects from the families
Carabidae, Gryllidae, Cicadellidae, Acrididae, Dryopthoidae, Scarabaeidae,
and Clubionidae, than did the translocation site (Table 2).
Diet
We collected 193 pellets from the pre-translocation site and 29 from the translocation
site. Forty-eight percent (10 of 21) of prey taxa that we trapped were
actually present in pellets. Prey items present in pellets but not in traps included
the families Cambaridae (crayfish), Curculionidae (beetles), Emydidae (turtles),
Ranidae (frogs), Spiraxidae (snails), and Soricidae (shrews). The Spearman’s
rank correlation revealed no significant correlation (ρ = 0.59, n = 10, P > 0.05)
between diet and prey abundance for any arthropod family. The critical P-value
at which independent samples t-tests were no longer considered significant for
diet was P > 0.025
Table 1. Insects trapped on three Florida Burrowing Owl study areas located on the Fort Green
Mine Site, Polk/Manatee counties, FL, May 2005–May 2006. P = present, X= not present.
Insect family Pre-Translocation Translocation
Acrididae P P
Carabidae P P
Cicadellidae P P
Clubionidae P P
Coreidae P X
Dryophthoridae P P
Gelastocoridae P P
Gryllidae P P
Gryllotalpidae P P
Hymenoptera P P
Labiduridae P P
Lepidoptera P P
Lycosidae P P
Mutillidae P P
Pentatomidae P X
Pseudophasatidae P X
Reduviidae P X
Scarabaeidae P P
Tettigoniidae P P
Theridiidae P X
760 Southeastern Naturalist Vol. 11, No. 4
Owls on the pre-translocation site consumed significantly more insects from
the families Gryllidae and Scarabaeidae, while owls on the translocation site
consumed more insects from the families Carabidae and Curculionidae (Tables
3, 4). Other than this, the diet of all other prey items was similar.
Table 2. Prey abundance of Florida Burrowing Owls by site in Polk and Manatee counties, FL, May
2005–May 2006. Number of sample periods (n) equals 16. Degrees-of-freedom for all analyses
equals 30.
Pre-translocation Translocation
Species Mean (±SE) Mean (±SE) T-statistic P-value
Carabidae 2.6 ± 0.40 1.1 ± 0.25 3.20 0.003
Gryllidae 5.2 ± 0.53 1.4 ± 0.51 5.09 <0.001
Cicadellidae 0.7 ± 0.15 0.1 ± 0.06 3.83 <0.001
Acrididae 4.4 ± 0.61 1.8 ± 0.46 3.43 0.002
Dryopthoridae 0.7 ± 0.18 0.2 ± 0.10 2.46 0.020
Scarabaeidae 13.1 ± 1.84 3.5 ± 1.08 4.51 <0.001
Clubionidae 8.8 ± 1.07 2.6 ± 0.48 5.28 <0.001
Gastrophyne 2.6 ± 0.72 0.0 3.56 0.001
Table 4. Number and percent total of prey items (identified to family) in pellets of Florida Burrowing
Owls by study site, Fort Green Mine Site, Polk/Manatee counties, FL, May 2005–May 2006.
Pre-translocation Translocation
Family Number Percent Number Percent
Acrididae 1174 21.5 128 19.7
Cambaridae 3 0.1 0 0.0
Carabidae 801 14.7 145 22.3
Clubionidae 134 2.4 15 2.3
Curculionidae 79 1.4 27 4.2
Emydidae 2 0.04 1 0.2
Gryllidae 1318 24.1 138 21.2
Gryllotalpidae 92 1.7 10 1.5
Labiduridae 430 7.9 65 10.0
Lycosidae 42 0.7 0 0.0
Microhylidae 9 0.2 0 0.0
Ranidae 5 0.09 0 0.0
Scarabaeidae 1328 24.3 110 16.9
Soricidae 3 0.05 1 0.2
Spiraxidae 6 0.2 4 0.6
Tettigoniidae 37 0.8 7 1.1
Total 3297 100 651 100
Table 3. Diet of Florida Burrowing Owls by site in Polk and Manatee counties, FL, May 2005–May
2006. Number of sample periods is (n) equals16. Degrees-of-freedom for all analyses equals 30.
Pre-translocation Translocation
Species Mean (±SE) Mean (±SE) T-statistic P-value
Carabidae 4.1 ± 0.10 5.8 ± 0.10 7.75 <0.001
Curculionidae 0.4 ± 0.10 1.1 ± 0.10 7.32 <0.001
Gryllidae 6.8 ± 0.10 5.5 ± 0.09 2.36 0.020
Scarabaeidae 6.9 ± 0.14 4.4 ± 0.14 5.60 <0.001
R.J. Sarno, P.A. Nixon, B.K. Mealey, 2012 R.E. Concoby, R.J. Mrykalo, and M.M. Grigione 761
Discussion
Relative prey richness among sites did not vary noticeably. Although we
trapped the greatest number of distinct arthropod groups on the pre-translocation
(non-mined) site, 6 of the families were absent from the diet of owls. The
insect families Carabidae, Curculionidae, Gryllidae, and Scarabaeidae were
the most important diet components of owls in our study, and many of these
same families appear to be important in the diet of A. c. hypugaea (Bonaparte)
(Western Burrowing Owl; Chipman et al. 2008, Marti 1974, Thomspon and
Anderson 1988).
Only 10 of 21 prey types that we trapped were actually present in owl pellets.
Except for the family Microhylidae, all remaining non-arthropod prey remains in
pellets were neither trapped nor observed dead outside of burrows. Perhaps our
trapping protocol prevented capture of these particular prey species and/or owls
regularly hunted in different habitats (Mrykalo et al. 2007, Sissons and Scalise
2001). For example, it appears that owls were hunting in aquatic habitats (i.e.,
creeks, ephemeral wetlands, and drainage ditches) due to the remains of frogs
(Ranidae and Microhylidae), turtles (Emydidae), and crayfish (Ca mbaridae).
The similarity in prey abundance and diet between the pre-translocation
and translocation sites suggests that reclaimed mines may serve as adequate
refugia for Florida Burrowing Owls. However, further studies are needed that
encompass a larger number of non-mined versus reclaimed sites to adequately
determine if reclaimed mined sites provide suitable foraging habitat for Florida
Burrowing Owls.
Given that owl diet can differ by season and sex (Hall et al. 2009, Marti 1974,
York et al. 2002), it is important that any potential translocation site contain
sufficient numbers of potential invertebrate and vertebrate prey that owls would
normally encounter while foraging. Additionally, since owls are central-place
foragers, and males generally forage farthest from burrows (Thompson and Anderson
1988), there is a need for adequate feeding areas at greater distances from
burrows. Therefore, the juxtaposition of translocation sites to a mosaic of different
habitat (at varying distances from the burrow) may increase the likelihood of
a successful translocation from a foraging perspective, given that owls appear to
be opportunistic feeders (Grimm et al. 1985).
Population projections prepared by the GeoPlan Center at the University of
Florida indicate that Florida’s human population will double in size from 17.9
million people to 35.8 million people between 2005 and 2060. As a result of human
population growth, nearly 2,833,000 ha of land will be developed. Of this,
approximately 1,012,000 ha of the highest priority land for conservation is likely
to be directly impacted (Barnett and Dobshinsky 2007). If viable Florida Burrowing
Owl populations are to be maintained, then translocation is likely to become
a more common conservation tool. Therefore, we suggest that wildlife managers
and/or researchers ascertain whether reclaimed sites that are targeted for translocation
of Florida Burrowing Owls support comparable numbers and variety of
invertebrate/vertebrate communities compared to non-mined sites.
762 Southeastern Naturalist Vol. 11, No. 4
Acknowledgments
We thank M. Baughman, B. Brooks, and R. Morris for assistance in the field. The
following agencies contributed to the success of this translocation: US Fish and Wildlife
Service, Florida Fish and Wildlife Conservation Commission, Florida Department of Environmental
Protection, Hillsborough County Upland Habitat Protection Division, Polk
County Environmental Department, Hardee County Biological Staff, IMC Phosphates
Company, Raptor Management Consultants, Biological Research Associates, Quest
Ecology, Penn Pro Engineering and the Wild at Heart Rehabilitation Center (Arizona).
Permission to translocate owls was granted to R.E. Concoby by the US Fish and Wildlife
Service and the Florida Fish and Wildlife Conservation Commission. Capture and tagging
permits were issued to L. Walton, R.E. Concoby, B.K. Mealey, and R.J. Sarno.
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